In a variety of circumstances, a wideband radio receiver may be employed to detect transmissions of signals within a wide (large) band of frequencies, such signals typically each having a bandwidth that is much narrower than the wide band. For example, it may be known that, or desired to detect whether, a signal or signals of narrow bandwidth, such as a carrier at any of a large number of possible frequencies, is or are being broadcast. Some or all of the potential carrier frequencies may be known, or all or some potential signals may be known, only to lie somewhere in a broad range of frequencies. Typically, wideband acquisition is used to detect the presence of such signals of interest. Then, narrowband acquisition and/or analysis techniques are used to isolate the signal(s) of interest from background or interfering signals (e.g., to improve the receiver's signal-to-noise ratio), and/or to configure an analysis receiver (often having a fixed bandwidth) to collect additional information such as to perform modulation detection/analysis and signal feature extractions from the detected transmissions. Thus, it may be desired to know when, or that, a signal is being broadcast within the wide band, and then to analyze and identify such signals as to their type, source, and/or content. Subsequently, analysis can determine whether a detected signal is new or was previously identified.
Various approaches have been used to accommodate narrowband detection within wide frequency ranges. For example, full digital narrowband channelization of a wide signal band may be implemented with a bank of digital filters to provide for the simultaneous filtering and detection of signals contained within different frequency sub-regions within the wide band. A wide detection band provides high probability of intercept, while the narrowband channelization filters provide for relatively higher sensitivity and system selectivity. Unfortunately, implementation of a large number of narrowband channels over a wide frequency range often requires a very large, perhaps even an excessive, number of digital filters, thus increasing the digital hardware, system size, power consumed and, sometimes, time required to implement the detection and analysis functions. This approach can be particularly inefficient when much of the wideband spectrum may contain few signals of interest or when signals are unevenly distributed.
Alternatively, the use of two receivers, namely a wideband channelizer/receiver and a separate, tunable narrowband channelizer/receiver, may be employed. The narrowband receiver is cued and tuned to a signal of interest only after a processor has processed the detected signals (often pulses) from the wideband channelizer. The latency (i.e., time consumed) to detect the pulses within the wideband window using the wideband channelizer and to then tune and configure the narrowband receiver can result in missing all or most of the opportunity to analyze (or even detect) fleeting emissions (i.e., signals from transmitters active only for short intervals, such as to send a quick, non-repeating pulse or burst of pulses). The separate narrowband analysis receiver also requires additional space and power, though generally less space and power than the plurality of narrowband receivers of the aforementioned type of system.
In another configuration, one or more fixed (rather than tunable) narrowband filters may be contained within a wideband channelizer/receiver. Each such narrowband filter may have a fixed bandwidth and frequency, and each narrowband filter typically has its own signal detection circuitry. Consequently, the wideband receiver must be re-tuned once a signal is detected in order to place the detected signal within the, or a, narrowband channel.
A need thus exists for an improved wideband receiver, preferably one in which by comparison with such prior approaches, requires less power. It is also preferable that it acquire signals quickly, to facilitate their analysis.